SAN MARCOS  Julie Mottershaw has never shied away from a challenge. She’s running a 2,300-student high school in a temporary campus amid a massive reconstruction project, after all.

But last fall she was dealt a challenge that no one wants. Mottershaw, 45, was diagnosed with Stage 4 cancer. That means it’s metastasized — the cancer has spread and is incurable, but manageable.

Last fall, as Mottershaw was entering her seventh year as principal at San Marcos High School, she fell ill with pneumonia-like symptoms. For the athletic and normally healthy Mottershaw, the three-months-long illness was exhausting and frustrating.

“I don’t think cancer was on anyone’s radar,” she said.

Mottershaw grew so weak that she stopped driving, and she was admitted to a hospital through the emergency room in late November. On Nov. 29, doctors told her that cancer was found in her lungs and liver, but that it was “breast cancer primary.”

She had just had a mammogram and ultrasound in August, with no indication of any problems. “I’d taken every health precaution to avoid getting breast cancer.”

Mottershaw began chemotherapy Dec. 5, and set out to face the illness head-on.

“I was raised to think I could do whatever I want to do. All I know is to fight and to give it 100 percent. As long as I know what I have to do, I can do it.”

She used the time off after the diagnosis and winter break to adjust her new routine: doctor appointments, weekly three-hour chemotherapy sessions, and exercising again, especially important to the former SDSU basketball player.

Since her students returned to school the second week of January, Mottershaw hasn’t missed a day. Her own daughter, Jordan, is a member of the Knights’ Class of 2013.

“Part of staying healthy is working,” Mottershaw said. “I love these kids. I love this school. I can’t imagine sitting at home right now. It would not be healthy. They inspire me every day.”

She said her doctor told her early on that she needed to think about going back to work, and at the time she was surprised.

“I could hardly walk,” Mottershaw said. “I can actually jog 2 miles now. I have a feeling he (the doctor) wants me to lead a normal life and thrive.

“I’ve been telling the kids here for years to demonstrate Knight Pride … responsibility and courage. I believe in those things as a way of life. I wasn’t going to be a hypocrite.”

San Marcos High students were told of Mottershaw’s cancer in December, and their support, as well as from parents and colleagues, was overwhelming, she said. Flowers, food, blankets, prayer lists, notes, texts, inspirational bracelets.

Mottershaw said assistance like prepared dinners are especially welcome for her and Jordan after a long drive home to Lakeside.

While district administrators were confident in Mottershaw’s ability to lead, they were ready to help at San Marcos High, a large comprehensive high school that’s about halfway through a rebuild.

“It’s turned out we haven’t had to do much of that,” said Nancy Peterson, a close friend and the district’s director of secondary curriculum. “She’s handled this whole thing with grace and determination. “It’s remarkable. She hasn’t missed a beat.”